The entire disclosure of Japanese Patent Application No. 2001-291803 filed on Sep. 25, 2001, the foreign priority Application, including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a glass bulb for a cathode ray tube to be used for e.g. a display for a television broadcast receiver (hereinafter referred to as a television) or a computer, and to a cathode ray tube employing said bulb.
2. Description of Related Art
A face portion 5 of a cathode ray tube has a substantially rectangular shape as illustrated in FIG. 10, as viewed from the direction of the tube axis 19 (arrow A in FIG. 2), and has two long sides 21 and two short sides 22. Further, the axis passing through the center 23 of the face portion 5 in parallel with the long sides 21, is referred to as the long axis 24, and the axis in parallel with the short sides 22 is referred to as the short axis 25.
As illustrated in FIG. 11, the panel 2, like the face portion 5, has four sides comprising two long sides 30 and two short sides 31 at its seal edge portion 7, and its outer profile has a shape substantially the same as the profile of the face portion 5.
Further, as illustrated in FIG. 12, the seal edge portion 8 of the funnel 3 likewise has two long sides 32 and two short sides 33, and has a shape substantially congruent with that of the seal edge portion 7 of the panel 2, as described above. Then, the seal edge portion 7 of the panel 2 and the seal edge portion 8 of the funnel 3 are joined and sealingly bonded by means of e.g. a solder glass, to form a sealing portion 34 (shown in FIG. 2).
In the cathode ray tube having a construction as described above in detail, inside of the bulb 1 is maintained to be in high vacuum in order to have the electron beam radiated to display picture images. However, the bulb 1 having an asymmetrical shape, as is different from a spherical shell, is loaded with a pressure difference of 1 atm between its inside and outside, whereby it is in an unstable state due to a high strain energy thus formed. Therefore, even when a very small crack is formed in the glass constituting the panel 2 or the funnel 3, it is likely that the crack grows to release the strain energy, which may lead to a destruction. Further, when a high tensile stress is formed on the outer surface of the panel 2 or the funnel 3, a delayed fracture may take place due to the effect of moisture in the atmosphere, which may cause decrease in the reliability of the cathode ray tube.
In recent years, liquid crystal displays and plasma displays have been developed and put into practical use, and when these are compared with a display employing a cathode ray tube, the large depth of the cathode ray tube is regarded as a demerit. Therefore, it has been tried to reduce the depth (the length in the direction of the tube axis 19) of a bulb to be employed in cathode ray tubes, and as a result, the asymmetricity of the shape of the bulb has further increased and the tensile stress formed on the outer surface of the bulb has increased.
The body portion 9 of the funnel 3 is formed to have a substantially truncated pyramid shape which has a large opening towards the panel 2, and accordingly, when the inside of the bulb 1 is vacuumed, the body portion 9 tends to be deformed as it is depressed towards the panel 2 in the direction of the tube axis 19. And, the face portion 5 of the panel 2, is formed to be most flat in the bulb 1 in order to display picture images, and thus is very likely to be deformed, and tends to be deformed so as to be depressed towards the funnel 3 in the direction of the tube axis 19. As a result, to the sealing portion 34 and the skirt portion 6 continuous therefrom, a force will be exerted to expand them outward (in the direction departing from the tube axis 19).
FIG. 13 shows an example of the distribution of the stress formed on the outer surface of the bulb 1. Here, when the distribution curve (indicated by a chain double-dashed line in the FIG.) is outside of the profile of the bulb 1, it indicates that a tensile stress is formed, and when the distribution curve is inside of the profile of the bulb 1, it indicates that a compressive stress is formed.
The left half of the solid line in FIG. 13 represents the outer profile line of the cross section when the bulb is cut along the long axis 24, and its right half represents the outer profile line of the cross section when the bulb is cut along the short axis 25. Further, in the following description, the tensile stress formed on the bulb surface when its inside is vacuumed, will be referred to as a xe2x80x9ctensile vacuum stressxe2x80x9d.
As illustrated in FIG. 13, a high tensile vacuum stress is formed at the end of the face portion 5 of the panel 2 and at the body portion 9 of the funnel 3. Accordingly, on the outer surface of the sealing portion 34 where the seal edge portion 7 of the panel 2 and the seal edge portion 8 of the funnel 3 are bonded, strains formed on both the panel 2 and the funnel 3, are propagated and concentrated to form an extremely high tensile vacuum stress. Especially, at the end portions of the short axis 25 of the face portion 5, namely in the vicinity of the center portions of the long sides 21, a high tensile vacuum stress is formed.
As a result, it may cause lowering of the safety due to destruction of the cathode ray tube, or lowering of the reliability due to the delayed fracture caused by moisture in the atmosphere. Further, if the wall thickness of the glass of the body portion 9 or of the seal edge portions 7 and 8, is increased in order to solve the problem of such a high tensile vacuum stress, there will be a problem of an increase of the mass, which is a major demerit for a cathode ray tube, as well as the problem of the depth.
It is an object of the present invention to prevent the increase of the tensile vacuum stress formed at the sealing portion without increasing the wall thickness of the glass at the body portion of the funnel or at the sealing portion of the panel and the funnel, and thereby to provide a glass bulb for a cathode ray tube, being light in weight and having a small depth and high safety, and to provide a cathode ray tube employing such a bulb.
FIG. 2 is a schematic view illustrating the cross section of a cathode ray tube. The cathode ray tube employs a glass bulb (hereinafter, a glass bulb for a cathode ray tube will be referred to simply as xe2x80x9ca bulbxe2x80x9d) 1 as an envelope, and the bulb 1 is constituted by a panel 2 and a funnel 3. The panel 2 comprises a face portion 5 having a screen 4 for displaying picture images, and a skirt portion 6 constituting a sidewall of the face portion 5. The skirt portion 6 has a seal edge portion 7 at its end.
Further, the funnel 3 has a seal edge portion 8 having a shape substantially congruent with the shape of the seal edge portion 7 of the panel 2, and the other opening portion is connected to a cylindrical neck portion 10, and a yoke portion 11 is integrally connected between the body portion 9 and the neck portion 10 to form a substantially funnel shape.
An electron gun 12 is housed in the neck portion 10, and an electron beam radiated from the electron gun 12 is deflected by a deflecting yoke 13 put around the yoke portion 11, and lets a phosphor screen 14 emit a light.
Besides these, an aluminum film 15 for reflecting the light emitted from the phosphor screen 14 forward, a shadow mask 16 for regulating the position of electron beam irradiation on the phosphor screen 14, stud pins 17 for fixing the shadow mask 16 to the inside of the panel 2, and an anode button 18 for preventing high electrostatic potential of the shadow mask 16 due to the electron beam and for conductive earthing to the outside, are, for example, provided. The seal edge portion 7 of the panel 2 and the seal edge portion 8 of the funnel 3 are sealingly bonded to each other. Further, the chain line 19 in FIG. 2 indicates the tube axis connecting the central axis of the neck portion 10 and the center of the face portion 5.
Further, the chain double-dashed line 20 in FIG. 2 indicates the reference line of the bulb 1. The reference line 20 means one defined as xe2x80x9can imaginary base line perpendicular to the tube axis of a funnel yoke portion, defined by means of a reference line gaugexe2x80x9d in Japan Electronics and Information Technology Industries Association (JEITA) standard ED-2134B.
To solve the above-mentioned problems, the present invention provides a glass bulb for a cathode ray tube, comprising a panel and a funnel sealed to each other at the respective seal edge portions to form a sealing portion; wherein
said panel comprises a face portion having a substantially rectangular screen, and a skirt portion constituting a sidewall of the face portion and having a seal edge portion at its end;
said funnel has a seal edge portion having a shape substantially congruent with the seal edge portion of said panel, as an opening portion of its body portion, and the other opening portion is connected to a cylindrical neck portion for housing an electron gun, and a yoke portion is integrally connected between said body and neck portions to form a substantially funnel shape;
when a straight line in parallel to the central axis of said neck portion, passing through the center of the inner surface of said face portion, is designated as the bulb""s central axis, then
the distance H from the center of the inner surface of said face portion to a point where the reference line of the funnel crosses the bulb""s central axis, and the diagonal length D of said screen, satisfy D/Hxe2x89xa73.3; and
in said sealing portion having a substantially rectangular cross sectional shape in the direction perpendicular to the bulb""s central axis, a bent portion bending towards the bulb""s central axis, is provided at least on a long side of the sealing portion.
In the bulb of the present invention, it is preferred that, among four sides of said sealing portion having a substantially rectangular cross section, when the side having a bent portion is designated as a bent side, the center of the bent portion and the center of the bent side are substantially at the same position, and the length Lf of the bent portion in the direction of the bent side is at least a half of the length L of the bent side.
Further, in the bulb of the present invention, it is preferred that, when a point at one third of the height of the body portion from the center of a side of the sealing portion, in the direction perpendicular to said side towards the neck portion, is designated as a body portion""s end vicinity point, and the central position of the skirt portion of the panel facing and sealed with said body portion, is designated as a skirt portion""s central point, then
at least a region between said body portion""s end vicinity point and said skirt portion""s central point, is the bent portion bending towards the bulb""s central axis.
The present invention further provides the glass bulb for a cathode ray tube, having the above-mentioned construction, wherein said funnel is provided with a plurality of the yoke and neck portions.
The present invention still further provides a cathode ray tube employing the above-mentioned glass bulb for a cathode ray tube.